Washing machine and washing method

ABSTRACT

A washing machine and a washing method thereof are disclosed, in which waste of washing water is reduced and washing efficiency is improved. The washing method includes the steps of determining the volume of laundry in a tub, setting a first water level for a preliminary washing stroke and a second water level for a main washing stroke based on the determined volume of laundry, carrying out the preliminary washing stroke using washing water of the first water level and steam, and converting the preliminary washing stroke into the main washing stroke based on washing water of the second water level depending on an inner temperature of the tub.

This application claims the benefit of the Korean Patent Application No.P2005-15829, filed on Feb. 25, 2005, which is hereby incorporated byreference as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a washing machine, and moreparticularly, to a washing machine using steam and a washing methodthereof.

2. Discussion of the Related Art

A washing machine is a representative electric home appliance thatwashes the laundry using detergent and water. The washing machine isclassified into a top loading washing machine and a front loadingwashing machine depending on the position where the laundry is loadedinto the washing machine.

Generally, the top loading washing machine includes a tub verticallystood to receive the laundry, a pulsator rotating in the tub to wash thelaundry, and a lid provided on the top of the washing machine to openand close the tub. The top loading washing machine washes the laundryusing friction between the laundry and a water stream generated byrotation of the pulsator. The top loading washing machine has advantagesin view of short washing duration, large capacity, and low cost.However, the top loading washing machine provided with the pulsator hasdrawbacks in that tangling of the laundry occurs and damage of thelaundry is relatively high.

The front loading washing machine generally includes a drum and a tubprovided in parallel with each other to receive the laundry, a pluralityof lifters provided in the drum to lift and drop the laundry when thedrum is rotated, and a door provided on a front surface of the washingmachine to open and close the drum. The front loading washing machinewashes the laundry by rotating the drum at low speed after puttingwater, detergent, and the laundry into the drum. The front loadingwashing machine has advantages in that damage of the laundry is smalland tangling of the laundry does not occur.

However, the above washing machines require a great volume of washingwater to carry out washing processes along with a long time taken tosupply/drain the washing water to/from the washing machine.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a washing machine anda washing method thereof, which substantially obviate one or moreproblems due to limitations and disadvantages of the related art.

An object of the present invention is to provide a washing machine and awashing method thereof, in which waste of washing water is reduced andwashing efficiency is improved.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, awashing method according to the present invention includes the steps ofdetermining the volume of laundry in a tub, setting a first water levelfor a preliminary washing stroke and a second water level for a mainwashing stroke based on the determined volume of laundry, carrying outthe preliminary washing stroke using washing water of the first waterlevel and steam, and converting the preliminary washing stroke into themain washing stroke based on washing water of the second water leveldepending on an inner temperature of the tub. The second water level forthe main washing stroke is higher than the first water level for thepreliminary washing stroke.

The step of carrying out the preliminary washing stroke based on washingwater of the first water level and the steam includes the steps ofdetermining whether the washing water of the first water leveldecreases, and resupplying the washing water into the tub if the washingwater of the first water level decreases.

The step of converting the preliminary washing stroke into the mainwashing stroke depending on the inner temperature of the tub includesthe step of stopping a steam generator from steaming if the innertemperature of the tub is higher than a reference temperature. Thereference temperature is set based on the volume of laundry.

In another aspect of the present invention, a washing machine includes atemperature sensor sensing an inner temperature of a tub, a steamgenerator supplying steam into the tub, and a controller setting a firstwater level for a preliminary washing stroke and a second water levelfor a main washing stroke based on the volume of laundry in the tub, andconverting the preliminary washing stroke based on washing water of thefirst water level and the steam into the main washing stroke based onwashing water of the second water level depending on the innertemperature of the tub.

In still another aspect of the present invention, a washing methodincludes the steps of determining the volume of laundry in a tub,setting a first water level for a preliminary washing stroke, a secondwater level for a main washing stroke, a preliminary washing duration,and a main washing duration based on the determined volume of laundry,carrying out the preliminary washing stroke using washing water of thefirst water level and steam during the preliminary washing duration, andconverting the preliminary washing stroke into the main washing strokebased on washing water of the second water level during the main washingduration.

In further still another aspect of the present invention, a washingmachine includes a water level sensor sensing a water level in a tub, asteam generator supplying steam into the tub, and a controller setting afirst water level for a preliminary washing stroke, a second water levelfor a main washing stroke, a preliminary washing duration and a mainwashing duration based on the volume of laundry in the tub, andsequentially carrying out the preliminary washing stroke based onwashing water of the first water level and the steam during thepreliminary washing duration and the main washing stroke based onwashing water of the second water level during the main washingduration.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a perspective view illustrating a washing machine according tothe present invention;

FIG. 2 is a sectional view illustrating the washing machine shown inFIG. 1;

FIG. 3A is a cutaway perspective view illustrating a steam generator ofthe washing machine shown in FIG. 1;

FIG. 3B is a cutaway perspective view illustrating another steamgenerator of the washing machine shown in FIG. 1;

FIG. 4 illustrates a nozzle assembly connected with a water supply hoseand a supply hose;

FIG. 5 is a block diagram illustrating elements required for a washingstroke according to the present invention;

FIG. 6 is a flow chart illustrating a washing method according to thefirst embodiment of the present invention; and

FIG. 7 is a flow chart illustrating a washing method according to thesecond embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

FIG. 1 is a perspective view illustrating a washing machine according tothe present invention, and FIG. 2 is a sectional view illustrating thewashing machine shown in FIG. 1. Referring to FIG. 1 and FIG. 2, a frontloading drum washing machine is exemplarily shown. The front loadingdrum washing machine includes a tub 200 provided in a case 100 toreceive washing water, and a drum 300 rotatably provided in the tub 200to receive the laundry. The tub 200 and the drum 300 are provided in ahorizontal direction. The present invention is not limited to the frontloading drum washing machine shown in FIG. 1 and FIG. 2. The presentinvention may be applied to a top loading pulsator washing machine inwhich the tub and the drum are provided in a vertical direction.

Hereinafter, the washing machine according to the present invention willbe described in more detail with reference to FIG. 1 and FIG. 2.Referring to FIG. 1 and FIG. 2, the case 100 of the washing machineincludes a base 110, a wall 120, and a top plate 130. The base 110constitute the bottom of the case 100. A damper 20 is provided on thebase 110 to support the tub 200 that will be described later. The wall120 is stood above the base 110 to form a space therein, where the tub200 is to be provided. The wall 120 constitutes a front surface, a rearsurface and both sides of the case 100. The top plate 130 is provided atan opened upper portion of the wall 120 to seal the inner space of thecase 100 formed by the wall 120 and the base 110.

A control panel 80 is provided on a top of the front surface of the wall120 or a top surface of the top plate 130 to allow a user to manipulatethe washing machine. Springs 10 are connected with the wall 120 or aninner surface of the top plate 130 to allow the tub 200 to be hungthereon. A loading hole 125 is formed on any one of the wall, forexample, the front surface of the wall 120 to take the laundry ‘m’ inand out. The loading hole 125 is opened and closed by a door 150 hingedon the front surface of the wall 120. The door 150 includes a door frame151 and a door glass 155. The door glass 155, as shown in FIG. 2, isprovided in a hole formed at the center of the door frame 151.Therefore, the user can view the inner portion of the washing machine,more specifically, the inner portion of the drum 300, through the doorglass 150. The drum 300 will be described later.

The tub 200 is provided in the inner space of the case 100. The tub 200is supported by the springs 10 and the damper 20 in a state that itfloats at the center of the inner space. The tub 200 is provided suchthat its opened front surface faces the loading hole 125 of the wall120. The washing water is supplied into the tub 200 and stored therein.

The drum 300 is rotatably provided in the inner space of the tub 200. Tothis end, a motor 250 is provided in the case 100 to rotate the drum300. An example of a shaft of the motor 250 directly fixed to the drum300 is shown in FIG. 2. In this case, the shaft is fixed to the rearsurface of the drum 300 by passing through the tub 200. Meanwhile,although not shown, the motor 250 may be provided to indirectly rotatethe drum 300. In this case, the drum 300 and the motor 250 may beconnected with each other by a power transmission member such as a belt.

A plurality of through holes 310 are formed along the circumference ofthe drum 300 as shown in FIG. 2. The washing water stored in the tub 200can enter the inner space of the drum 300 through the through holes 310.As shown in FIG. 1 and FIG. 2, a plurality of lifters 320 are projectedfrom the inner circumference of the drum 300. The lifters 320 lift andthen drop the laundry ‘m’ when the drum 300 is rotated.

As shown in FIG. 2, a gasket 25 is provided between the tub 200 and thefront surface of the wall 120. The gasket 25 prevents the washing waterand the laundry ‘m’ in the tub 200 from leaking out of the tub 200 andentering the inner space of the case 100. Meanwhile, a nozzle assembly60 is provided at an upper portion of the gasket 25 to pass through thegasket 25. The nozzle assembly 60 will be described later.

A water supply valve 400 is provided at one side of the case 100, forexample, the rear surface of the wall 120, as shown in FIG. 1 and FIG.2. The water supply valve 400 is connected with an outer water supplysource, for example, a tap, and controls the washing water supplied fromthe water supply source. In the washing machine according to the presentinvention, the water supply valve 400 includes at least two valves,i.e., a first valve 410 and a second valve 420.

The first valve 410 is connected with the tub 200 through a first hose,for example, a water supply hose 510. The second valve 420 is connectedwith the tub 200 through a second hose, for example, a supply hose 520.As shown in FIG. 1, the second hose, i.e., the supply hose 520communicates the water supply valve 400 with the tub 200 through a pathdifferent from that of the first hose, i.e., the water supply hose 510.

The water supply valve 400 supplies water into the tub 200 through twohoses having paths different from each other as above, i.e., the watersupply hose 510 and the supply hose 520. The water supply valve 400 cansimultaneously or separately control the first valve 410 and the secondvalve 420. Thus, the water supply to the tub 200 through the watersupply hose 510 and the water supply to the tub 200 through the supplyhose 520 can be carried out simultaneously or separately.

The water supply hose 510 that communicates the first valve 410 with thetub 200 passes through a detergent box 50 as shown in FIG. 1. The watersupply hose 510 may be provided to directly pass through the detergentbox 50. Alternatively, the water supply hose 510 may communicate with apart of the detergent box 50 so that it is supplied with the detergentfrom the detergent box 50. Therefore, the washing water flown to thewater supply hose 510 through the first valve 410 is supplied into thetub 200 after always passing through the detergent box 50. The washingwater supplied into the tub 200 through the water supply hose 510 flowsdown along the inner surface of the tub 200 and is collected in thebottom of the tub 200. Meanwhile, the first valve 410 and the watersupply hose 510 communicating with the detergent box 50 may be providedin large numbers as shown in FIG. 1. In such case, the detergent forwashing and the detergent for rinsing can respectively be supplied intothe tub 200 at a timing interval.

The supply hose 520 that communicates the second valve 420 with the tub200 detours the detergent box 50 as shown in FIG. 1. Instead, the supplyhose 520 passes through a tank 610, for example. The tank 610 stores apredetermined volume of water or overflows the water stored therein tosupply the water into the tub 200. Further, the tank 610 may supply thepredetermined volume of water stored therein into the tub 200 at onetime. The supply hose 520 passing through the tank 610, as shown in FIG.2, is connected with the nozzle assembly 60 provided to pass through thegasket 25. Therefore, the washing water flown to the supply hose 520through the second valve 420 is supplied into the tub 200 after alwayspassing through the tank 610.

Meanwhile, it is possible to obtain higher washing effect when thelaundry is washed using heated water than washing effect obtained whenthe laundry is washed using cold water. Therefore, in the washingmachine according to the present invention, a steam generator 600 isprovided as shown in FIG. 1 and FIG. 2 so that hot steam is suppliedinto the tub 200 to enhance the washing effect. To allow the steamgenerator 600 to supply the steam into the tub 200, a water tank storingwater supplied from the water supply source, a heater heating the waterstored in the water tank, and a path connecting the water supply source,the water tank and the tub 200 with one another are required.

The washing machine according to the present invention are provided withthe second hose, i.e., the supply hose 520 connecting the water supplyvalve 400 with the tub 200 and the tank 610 provided at a middle portionof the supply hose 520 to store the water therein. Therefore, toefficiently use the inner space of the washing machine and reduce thenumber of parts, the tank 610 and the supply hose 520 are used as theparts of the steam generator 600.

In the present invention, the steam generator 600 that uses the tank 610and the supply hose 520 as its parts can supply the washing watersupplied from the second valve 420 into the tub 200 through the nozzleassembly 60 in a liquid or steam state. FIG. 3A and FIG. 3B illustratethe steam generator 600 in detail, and FIG. 5 illustrates elementsrelated to water supply. Hereinafter, the steam generator 600 will bedescribed in more detail.

The steam generator 600, as shown in FIG. 3A, includes the tank 610having an inlet 520 and an outlet 630, a heater 640 provided on thebottom inside the tank 610, a sensor assembly 650 sensing a water levelin the tank 610, and at least one temperature sensor 617 sensing atemperature inside the tank 610.

The tank 610 has a space therein, which can receive a predeterminedvolume of water. A flange 611 and an extension 612 are formed on anouter surface of the tank 610 to fix the tank 610 to the inner surfaceof the case 100. The inlet 620 and the outlet 630 are formed at an upperportion of the tank 610. This is to prevent the water in the tank 610from flowing backward toward the second valve 420 through the inlet 620and effectively drain out the steam generated in the tank 610 throughthe outlet 630. Portions of the tank 610 where the inlet 620 and theoutlet 630 are formed are locally projected as shown in FIG. 1 and FIG.3A.

The inlet 620 communicates with the second valve 420 through the supplyhose 520 while the outlet 630 communicates with the nozzle assembly 60through supply hose 520. Meanwhile, the inlet 620 and the outlet 630 arenot provided with a separate on/off valve. Therefore, the inlet 620 cancounteract the outlet 630 and vice versa. For example, the inlet 620 maybe used as the outlet while the outlet 630 may be used as the inlet. Insuch case, when the position of the tank 610 should be changed in thecase 100, the inlet 620 and the outlet 630 are used to be compatiblewith each other. Thus, the tank 610 can be used for different models.However, the outlet 630 and the inlet 620 may respectively be providedwith an on/off valve as occasion demands.

The heater 640 includes a radiator 641 and a terminal 645. The radiator641 of the heater 640, as shown in FIG. 3A, is uniformly provided on thebottom inside the tank 610. The terminal 645 of the heater 640 isexposed to the outside after passing through the side of the tank 610.Meanwhile, one end of the radiator 641 is supported in a state that itis spaced apart from the bottom of the tank 610 at a predetermineddistance by a clamp 615 provided on the bottom of the tank 610.

The sensor assembly 650 includes a plurality of electrodes that sense aminimum water level and a full water level in the tank 610. The minimumwater level is to prevent the radiator 641 of the heater 640 from beingoverheated. The minimum water level is determined at the position alittle higher than the top of the radiator 641 to prevent the radiator641 from being exposed. The full water level is to prevent the watersupplied into the tank 610 from being overflown through the outlet 630.The full water level is determined at the position a little lower thanthe outlet 630.

The sensor assembly 650 that senses the minimum water level and the fullwater level includes a common electrode 651, a first electrode 653, anda second electrode 655, as shown in FIG. 3A. The common electrode 651,the first electrode 653, and the second electrode 655 are verticallyarranged in a state that they are spaced apart from one another at apredetermined distance. Top ends of the electrodes are provided to passthrough the top surface of the tank 610. Terminals are respectivelyformed on the top ends of the electrodes exposed by passing through thetank 610.

The common electrode 651 and the first electrode 653, as shown in FIG.3A, are long and their heights are substantially the same as each other.Therefore, the common electrode 651 and the first electrode 653 aresimultaneously soaked in the water or exposed from the water. If thecommon electrode 651 and the first electrode 653 are simultaneouslysoaked in the water, the common electrode 651 and the first electrode653 are electrically connected with each other. Thus, a controller 700such as a microprocessor determines that the water level in the tank 610is higher than the minimum water level.

By contrast, if the common electrode 651 and the first electrode 653 aresimultaneously exposed from the water as the water level in the tank 610decreases, the common electrode 651 and the first electrode 653 areelectrically disconnected from each other. Thus, the controller 700determines that the water level in the tank 610 is lower than theminimum water level. If the water level in the tank 610 is lower thanthe minimum water level, the controller 700 stops the operation of theheater 640 to prevent the heater 640 from being damaged by overheat.

The second electrode 655 is shorter than the common electrode 651 andthe first electrode 653. Therefore, a lower end of the second electrode655 is positioned to be higher than lower ends of the common electrode651 and the first electrode 653. If the second electrode 655 is notsoaked in the water as the water level in the tank 610 is low, thecommon electrode 651 and the second electrode 655 are electricallydisconnected from each other. Thus, the controller 700 determines thatthe water level in the tank 610 does not reach the full water level.

By contrast, if the second electrode 655 is soaked in the water as thewater level in the tank 610 increases, the common electrode 651 and thesecond electrode 655 are electrically connected with each other. Thus,the controller 700 determines that the water level in the tank 610reaches the full water level. If the water level in the tank 610 reachesthe full water level, the controller 700 closes the second valve 420 tostop the water from being supplied into the tank 610 when the steamgenerator 600 generates steam. However, the controller 700 does notclose the second valve 420 even if the sensor assembly 650 senses thefull water level when the water is supplied into the tub 200 through thesteam generator 600. Thus, the water continues to be supplied into thetank 610. As a result, the water supplied into the tank 610 is overflownfrom the tank 610 so that the water can be supplied into the tub 200through the outlet 630.

Hereinafter, the procedure of generating steam through theaforementioned steam generator 600 will be described in brief. First,the controller 700 measures the water level in the tank 610 using thesensor assembly 650. If the water level in the tank 610 is low, thecontroller 700 opens the second valve 420 to supply the washing waterinto the tank 610. However, if the sensor assembly 650 senses the fullwater level, the controller 700 closes the second valve 420 to stop thewashing water from being supplied into the tank 610.

If the tank 610 is filled with the washing water, the heater 640 isoperated to heat the washing water in the tank 610. If the washing wateris heated, steam is generated. The generated steam is sprayed into thetub 200 through the outlet 630. The water level in the tank 610 isgradually lowered as the steam continues to be supplied into the tub200. If the washing water in the tank 610 is evaporated to allow thewater level in the tank 610 to reach the minimum water level, thecontroller 700 turns the heater 640 off. If necessary, the controller700 turns again the heater 640 on to supply the steam into the tub 200after supplying the washing water into the tank 610.

The case where the water in the tank 610 is supplied into the tub 200through the outlet 630 as the water in the tank 610 overflows has beendescribed as above. However, the present invention is not limited tosuch case. As another example, the water stored in the tank 610 may besupplied into the tub 200 at one time if the water in the tank 610reaches the full water level. To this end, as shown in FIG. 3B, a secondoutlet 660 that can be turned on/off is provided at a lower portion ofthe tank 610. The second outlet 660 is connected with the supply hose520 connected with the tub 200. The second outlet 660 constructed asabove is usually closed. The second outlet 660 is selectively opened tosupply the washing water stored in the tank 610 into the tub 200 at onetime only when the user intends to supply the washing water into the tub200 while measuring the volume of the washing water.

Meanwhile, as shown in FIG. 2, a drain 210 is formed at the lowerportion of the tub 200. The drain 210 is connected with a bellows tube33. The bellows tube 33 is connected with a pump unit that pumps thewater supplied into the tub 200 through the drain 210 and the bellowstube 33 to drain the water out or circulates the water in the drum 300.

The pump unit, as shown in FIG. 1, includes a pump housing 45, acirculating pump 30, and a drain pump 40. The pump housing 45 issupplied with the water passing through the drain 210 and the bellowstube 33. The drain pump 40 is connected with a drain hose 37 thatcommunicates with the outside. The drain pump 40 drains the washingwater supplied into the pump housing 50 out through the drain hose 37during a drain stroke of the washing machine.

The circulating pump 30 is connected with a circulating hose 35. Thecirculating hose 35 is connected with the nozzle assembly 60 of whichone end is provided to pass through the gasket 25 as shown in FIG. 2.The circulating pump 30 pumps the washing water supplied into the pumphousing 45 toward the circulating hose 35 during washing and rinsingstrokes of the washing machine. The pumped washing water is sprayed intothe tub 200 through the nozzle assembly 60.

As described above, the nozzle assembly 60 provided to pass through thegasket 25 is connected with the circulating hose 35 and the supply hose520, respectively. The nozzle assembly 60, as shown in FIG. 4, includesa first nozzle 61 connected with the circulating hose 35 to spray thewashing water pumped by the circulating pump 30 into the tub 200, and asecond nozzle 62 connected with the supply hose 520 to spray the steamgenerated by the steam generator 600 or the washing water passingthrough the steam generator 60 into the tub 200. The first nozzle 61 andthe second nozzle 62, as shown in FIG. 4, are arranged in parallel witheach other and formed in a single body to facilitate their manufactureand arrangement.

Meanwhile, in the present invention, the washing water is supplied intothe tub 200 through the supply hose 520 that detours the detergent box50 as well as the water supply hose 510 that passes through thedetergent box 50. Therefore, a greater volume of the washing water canbe supplied into the tub 200 within a shorter time in comparison withthe related art washing machine that supplies the water only through thewater supply hose 510.

Hereinafter, embodiments of a water supply method according to thepresent invention will be described in detail.

FIRST EMBODIMENT

FIG. 6 is a flow chart illustrating a washing method according to thefirst embodiment of the present invention. Referring to FIG. 6, if awashing stroke starts, the controller 700 senses the volume of thelaundry (S10). The controller 700 repeatedly rotates the drum 300 inforward and reverse directions to sense the volume of the laundry. Thecontroller 700 determines the volume of the laundry based on load androtational speed of the drum 300 detected when the drum 300 is rotated.Another methods of determining the volume of the laundry may be appliedto the present invention.

If the volume of the laundry is determined, the controller 700 selectsvarious washing options depending on the volume of the laundry (S20).For example, the controller 700 can determine the volume of the washingwater (first water level) to be used for a preliminary washing stroke,the volume of the washing water (second water level) to be used for amain washing stroke, duration of the washing stroke, a number oftimes/duration of a rinsing stroke, a number of times/duration of adehydrating stroke, and so on based on the volume of the laundry. Thepreliminary washing stroke is to sufficiently soak the laundry using asmall volume of washing water and increase an inner temperature of thetub 200 and a temperature of the washing water using steam. The mainwashing stroke is to normally wash the laundry. Since the first waterlevel is lower than the second water level, the washing water in themain washing stroke should be resupplied into the tub 200. Thecontroller 700 can determine the volume (second water level minus firstwater level) of the washing water to be resupplied in the main washingstroke. Optionally, the controller 700 can set a reference temperature Tused for the preliminary washing stroke, duration of the preliminarywashing stroke, duration of the main washing stroke, the volume of thewashing water supplied to the steam generator 600, driving duration ofthe heater 640, and so on depending on the volume of the laundry.

If various options are selected, the washing water is supplied into thetub 200 by the first water level. To this end, the controller 700 opensthe first valve 410 to supply the washing water of the water supplysource into the tub 200 through the water supply hose 510. The watersupply hose 510 passes through the detergent box 50 as mentioned above.Therefore, if there is the detergent in the detergent box 50, thedetergent is supplied into the tub 200 along with the washing waterflown into the water supply hose 510. The washing water supplied intothe tub 200 through the water supply hose 510 flows down along the innersurface of the tub 200 and is collected in the bottom of the tub 200.With the lapse of time, the water level in the tub 200 graduallyincreases. At the same time, the controller 700 opens the second valve420 to supply the washing water to the steam generator 600. The washingwater flown into the supply hose 520 is supplied into the tank 610 ofthe steam generator 600. With the lapse of time, the tank 610 is filledwith the washing water.

While the washing water is supplied into the tank 610, the sensorassembly 650 of the steam generator 600 senses the water level in thetank 610. If the water level in the tank 610 reaches the full waterlevel, the controller 700 closes the second valve 420. The controller700 turns the heater 600 on for a set time, for example, several secondsor several tens of seconds to heat the washing water in the tank 610. Ifthe washing water in the tank 610 starts to boil, the steam is generatedand the pressure in the tank 610 increases. The controller 700 turns theheater 640 off after the lapse of the set time.

While the washing water is supplied into the tub 200, a main water levelsensor 330 repeatedly senses the water level of the washing waterflowing into the tub 200. The main water level sensor 330 converts theweight or pressure of the washing water in the tub 200 into a frequencysignal and transmits the frequency signal to the controller 700. Thecontroller 700 determines the water level of the washing water based onthe frequency signal transmitted from the main water level sensor 330.The controller 700 closes the first valve 410 if the sensed water levelreaches the first water level. For example, supposing that the waterlevel frequency corresponding to the first water level is in the rangeof 1000 kHz to 1200 kHz, the controller 700 closes the first valve 410when the frequency signal transmitted from the main water level sensor330 reaches 1000 kHz to 1200 kHz.

If the washing water in the tank 610 is boiled and the water level inthe tub 200 reaches the first water level, the controller 700 suppliesthe steam into the tub 200 and at the same time rotates the drum 300. Inother words, the controller 700 carries out the preliminary washingstroke using the steam and the washing water of the first water level(S30).

In addition, since the laundry absorbs the water during the preliminarywashing stroke, the water level in the tub 200 may be lowered. If thewater level in the tub 200 becomes lower than the first water level, thecontroller 700 resupplies the washing water into the tub 200. Forexample, if the frequency signal transmitted from the main water levelsensor 330 is lower than 1000 kHz, the controller 700 resupplies thewashing water into the tub 200 at a certain volume.

While the preliminary washing stroke is carried out, a temperaturesensor 800 provided in the tub 200 repeatedly senses the innertemperature of the tub 200. Then, the controller 700 compares the sensedinner temperature ‘t’ with a previously set temperature ‘T’ (S40). Ifthe inner temperature ‘t’ sensed by the temperature sensor 800 is lowerthan the previously set temperature ‘T,’ the controller 700 continues todrive the heater 640 and maintains the preliminary washing stroke. Inother words, the preliminary washing stroke using the steam ismaintained until the sensed inner temperature ‘t’ reaches the previouslyset temperature ‘T.’ The heater 640 is set to be driven for a previouslyset time. However, the heater 640 is driven again if the sensed innertemperature ‘t’ is lower than the previously set temperature ‘T.’

Afterwards, if the sensed inner temperature ‘t’ reaches the previouslyset temperature ‘T,’ the controller 700 stops driving of the steamgenerator 600 to prevent the steam from being supplied into the tub 200(S50). The controller 700 converts the preliminary washing stroke intothe main washing stroke. To carry out the main washing stroke, thecontroller 700 simultaneously opens the first valve 410 and the secondvalve 420 and supplies the washing water into the tub 200 through thewater supply hoses 510 and 520 until the water level in the tub 200reaches the second water level (S60).

If the water level in the tub 200 reaches the second water level, thecontroller 700 carries out the main washing stroke for a set duration ofthe main washing stroke (S70˜S80).

SECOND EMBODIMENT

FIG. 7 is a flow chart illustrating a washing method according to thesecond embodiment of the present invention. Referring to FIG. 7, if awashing stroke starts, the controller 700 determines the volume of thelaundry (S110) and selects various washing options depending on thevolume of the laundry (S120). For example, the controller 700 can setthe volume of the washing water (first water level) to be used for thepreliminary washing stroke, the volume of the washing water (secondwater level) to be used for the main washing stroke, number oftimes/duration of the rinsing stroke, number of times/duration of thedehydrating stroke, duration of the preliminary washing stroke (firstset time), duration of the main washing stroke (second set time), and soon depending on the volume of the laundry.

Then, the controller 700 carries out the preliminary washing strokeusing the steam and the washing water of the first water level duringthe preliminary washing stroke duration (first set time) (S130˜S140). Ifthe preliminary washing stroke duration passes, the controller 700converts the preliminary washing stroke into the main washing stroke.

To convert the preliminary washing stroke into the main washing stroke,the controller 700 stops the steam from being supplied into the tub 200(S150) and supplies the washing water into the tub 200 through the watersupply hoses 510 and 520 until the water level in the tub 200 reachesthe second water level (S160).

If the water level in the tub 200 reaches the second water level, thecontroller 700 carries out the washing stroke during the set duration ofthe main washing stroke (second set time) (S170˜S180).

In the present invention, the washing stroke has been described. Thepresent invention may be applied to a soaking stroke and a rinsingstroke. For example, the rinsing stroke of the present invention mayinclude a preliminary rinsing stroke based on a small volume of washingwater and steam and a main rinsing stroke based on a large volume ofwashing water.

As described above, since the small volume of the washing water is usedfor the preliminary washing stroke, the concentration of the detergentcontained in the washing water is high. Since the temperature in the tuband the temperature of the washing water are increased using the steam,washing efficiency is improved. Moreover, since the large volume of thewashing water is used for the main washing stroke, it is possible toeasily separate the laundry from contaminants.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A washing method comprising the steps of: determining the volume oflaundry in a tub; setting a first water level for a preliminary washingstroke and a second water level for a main washing stroke based on thedetermined volume of laundry; carrying out the preliminary washingstroke using washing water of the first water level and steam; andconverting the preliminary washing stroke into the main washing strokebased on washing water of the second water level depending on an innertemperature of the tub.
 2. The washing method as claimed in claim 1,wherein the second water level for the main washing stroke is higherthan the first water level for the preliminary washing stroke.
 3. Thewashing method as claimed in claim 1, further comprising the step ofsetting a driving duration of a steam generator that generates steam andthe volume of washing water supplied to the steam generator.
 4. Thewashing method as claimed in claim 1, wherein the step of carrying outthe preliminary washing stroke using washing water of the first waterlevel and steam includes the steps of: determining whether the washingwater of the first water level decreases; and resupplying the washingwater into the tub if the washing water of the first water leveldecreases.
 5. The washing method as claimed in claim 1, wherein the stepof converting the preliminary washing stroke into the main washingstroke depending on the inner temperature of the tub includes the stepof stopping the steam generator from steaming if the inner temperatureof the tub is higher than a reference temperature.
 6. The washing methodas claimed in claim 5, wherein the reference temperature is set based onthe volume of laundry.
 7. A washing machine comprising: a temperaturesensor sensing an inner temperature of a tub; a steam generatorsupplying steam into the tub; and a controller setting a first waterlevel for a preliminary washing stroke and a second water level for amain washing stroke based on the volume of laundry in the tub, andconverting the preliminary washing stroke based on washing water of thefirst water level and the steam into the main washing stroke based onwashing water of the second water level depending on the innertemperature of the tub.
 8. The washing machine as claimed in claim 7,wherein the controller sets the second water level to be higher than thefirst water level.
 9. The washing machine as claimed in claim 7, whereinthe controller further sets a driving duration of the steam generatorand the volume of washing water supplied to the steam generator based onthe volume of laundry.
 10. The washing machine as claimed in claim 7,wherein the controller determines whether the washing water of the firstwater level decreases during the preliminary washing stroke andresupplies the washing water into the tub if the washing water of thefirst water level decreases.
 11. The washing machine as claimed in claim7, wherein the controller stops the steam generator from steaming if theinner temperature of the tub is higher than a reference temperature andconverts the preliminary washing stroke into the main washing stroke.12. The washing machine as claimed in claim 11, wherein the controllersets the reference temperature based on the volume of laundry.
 13. Awashing method comprising the steps of: determining the volume oflaundry in a tub; setting a first water level for a preliminary washingstroke, a second water level for a main washing stroke, a preliminarywashing duration, and a main washing duration based on the determinedvolume of laundry; carrying out the preliminary washing stroke usingwashing water of the first water level and steam during the preliminarywashing duration; and converting the preliminary washing stroke into themain washing stroke based on washing water of the second water levelduring the main washing duration.
 14. The washing method as claimed inclaim 13, wherein the second water level for the main washing stroke ishigher than the first water level for the preliminary washing stroke.15. The washing method as claimed in claim 13, further comprising thestep of setting a driving duration of a steam generator that generatessteam and the volume of washing water supplied to the steam generator.16. The washing method as claimed in claim 13, wherein the step ofcarrying out the preliminary washing stroke using washing water of thefirst water level and steam during the preliminary washing durationincludes the steps of: repeatedly determining whether the washing waterof the first water level decreases; and resupplying the washing waterinto the tub if the washing water of the first water level decreases.17. A washing machine comprising: a water level sensor sensing a waterlevel in a tub; a steam generator supplying steam into the tub; and acontroller setting a first water level for a preliminary washing stroke,a second water level for a main washing stroke, a preliminary washingduration and a main washing duration based on the volume of laundry inthe tub, and sequentially carrying out the preliminary washing strokebased on washing water of the first water level and the steam during thepreliminary washing duration and the main washing stroke based onwashing water of the second water level during the main washingduration.
 18. The washing machine as claimed in claim 17, wherein thecontroller sets the second water level to be higher than the first waterlevel.
 19. The washing machine as claimed in claim 17, wherein thecontroller further sets a driving duration of the steam generator andthe volume of washing water supplied to the steam generator based on thevolume of laundry.
 20. The washing machine as claimed in claim 17,wherein the controller determines whether the washing water of the firstwater level decreases during the preliminary washing stroke andresupplies the washing water into the tub if the washing water of thefirst water level decreases.